23 comments on “Bering Sea Basalt Province

  1. Wow, now that’s interesting, that would explain some things. If I remember right, the Kuril-Kamchatka Trench used to be an active subduction zone far further to the NE, and I’ve always wondered why the part north of the triple junction has become inactive. At that time, the northern boundary of the Pacific plate must have been much further N as well, with that plate moving NW, or almost N, into Russia. Now, if the Bering block was squeezed out westward that might have halted any northern progress of the PA plate. So the PA plate began subducting more south, creating the AL trench and Islands. That way it stopped subducting at the northern part of the Ku-Ka Trench as well.

    Looking at the sea ground features, this would also explain the last kink in the Emperor chain, which now turns NW for its last 400 km from going almost N before. Suppose it has gone north before, then what is now the Shirshov Ridge could have been its continuation north into northern Siberia… I just read that reseach has found the ends of the Shirshov R. to be of different ages but could not access the paper as sci-hub is down… Hope they get up again, otherwise, perhaps – DFM? (DOI: 10.1134%2FS000143700705013X)

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    • Howdy Granyia –

      Interesting. Hadn’t followed the thought trail that far.

      I’m still trying to figure out what caused the scorpion’s tail in the Bering Sea north of Amchitka / Little Sitkin / Semisopochnoi / Kiska Islands. Stay warm. Cheers –

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  2. Very puzzled by the lack of correlation between the bouts of tremor at Agung, which seem pretty periodic, and the lack of associated eruptive activity on the webcam. Given that the tremor is meant to be caused by bubble nucleation and/or magma wagging as it moves up through the system (which by definition happens at pretty shallow levels) I wonder where all the gas and magma is going. The two seem to contradict each other. Normally when a system is open and the magma contains little gas, then you don’t get such significant tremor, sometimes none at all, and you see a sustained effusive eruption of a lava field. But the tremor indicates there must be a good deal of gas involved, so you would expect a lot of fragmentation, more akin to Etna’s SE crater, yet we are not seeing that.
    Nor are we seeing anything like Shinmoedake, where a sticky lava lake (or very runny lava dome – take your pick) trapped enough gas for large bubbles to form that then popped in dramatic vulcanian bursts. So the webcam indicates that either the system has low gas content (maybe because it is currently still pushing out old magma that has had time to degas), or it is degassing easily without any associated explosions (this implies that the gas bubbles don’t have time to coalesce before getting released – an indication of hot mafic gas lava with very low gas content), or that the volcano actually hasn’t really started erupting properly yet and the related gas is still contained in its system. Of these three, and looking at the 1964 eruption, I think the latter is the most likely scenario. The eruption might of course still stall and the volcano will go back to sleep, even in this scenario.
    The other possibility is that the periodic tremor is caused by geothermal activity that (like a geyser) takes a few hours to reach a critical point before boiling off for an hour or so. Given the rains, this could also be the case and would explain the periodicity in the tremor.

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  3. Looking through comments elsewhere it appears the second scenario is the right one. The crater is filling with fresh lava that is obviously degassing in a non-explosive way, implying pretty hot/low crystalline/low gas (or any combination thereof) magma.

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    • Albert’s piece on the 1963 eruption said that perhaps a month of lava flows, explosions, and some PFs preceded the major aerial and pyroclastic activity. Might still be on track for a reprise 54 years after the last one. Cheers –

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      • Hi Agimarc, another great piece by the way. I love the way you try to puzzle out the tectonics behind these things. Your output is prodigious! wonderful stuff.
        Re Agung, I agree that a reprise of 1963 is definitely on the cards. I was just wondering how the mechanics behind it all work. Ignoring the initial phreatic throat clearing, the lava getting extruded now must already be gas depleted or be so hot and low crystalline that it can degas in a non-explosive way. I don’t know which it is. One possibility is that as the magma cools (crystallises) it stops degassing so easily allowing bubbles to coalesce and finally explode in a bigger eruption. Another possibility is that this first batch of magma is “old” magma that is gas-depleted and once it is gone, gas-rich magma from the new intrusion gets erupted in a more explosive eruption. Or maybe it is some combination of both. The intensity of the tremor suggests there is a lot of bubble nucleation at shallow levels.. so where is all this gas going? I can’t quite get my head around it.

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        • Howdy Bruce –

          Thank you for the kind words.

          Also trying to figure out how Agung works. We have a lot of pieces and a model (the 1963) eruption, though as far as I can tell nobody did an analysis of why that eruption proceeded as it did.

          Pieces:

          – Possible magma sheets (stacked dikes) in the conduit (from Unzen)
          – Hot magma interacting with water in and / or near the top of the crater
          – Phreatic eruption
          – Lots of water in the form of local rains
          – Lava in the crater
          – Continuing tremor

          I am thinking the shape of the magma intrusion up the conduit has a lot to do with what is going on. Don’t know how. Am also scratching my head about batching of magma in the system. If the magma is relatively viscous, we are not going to see a lot of mixing as the new intrusion mixes with the old. Rather you get the relatively shallow old stuff pushed up by the new like a plug or a cork or Pelee on Martinique. But that early stuff doesn’t present as a liquid. Problem is that at Unzen we saw that what was left after the last eruption cooled pretty quickly. Think that old stuff being pushed by new, hotter, more gas-laden new magma is a decent opening bid, but what happens after that? This would also suggest that the old magma is relatively gas depleted. Once the lid is off, the system opens up and we get a pretty intense eruption. Would submit that the system is not open yet.

          Enough early Sunday arm-waving. Lots of food for thought from this one. Cheers –

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          • looks like it is about to get interesting at Agung. Plot now showing distinct tornillos, despite the pathway being supposedly open and a rather flat lava dome now half-filling the crater.. looks like the explosive stuff is on the way to the surface like a rerun of the 1963 eruption. I guess it is all just a question of relative volumes at this stage as to whether it gets as big as 1963 again or fizzles out beforehand.

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            • Hmm… I don’t see tornillos. I see lots of Volcano-Tectonic, some Spasmodic Tremor, background noise. Tornillos are not supposed to have such high-amplitude P-S-wave onsets as VTs have. Have you saved a sample? Below is what I see at the moment.

              As to the explosive stuff: Do you not think that the 1963 explosive part was caused by the eruption of andesite following an initial flow of basalt?

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              • You might be right.. I thought I saw a couple in there when I looked, long tailed numbers, like the small one dead center in your screen shot between the two larger quakes.

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            • Maybe these are, in the lines ending at 14 and 14:30 UTC? Would be nice if someone knowledgeable could confirm or dismiss…

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    • I was surprised too reading yesterday’s report: “Satellite data also indicate that eruption of lava is ongoing within the summit crater. These data have recorded high temperatures consistent with new lava within the crater on 27, 28 and 29 November 2017. The volume of lava in the crater is currently about 20 million cubic meters, equivalent to about a third of the total crater volume.” That is quite lot of piling up in the crater. So perhaps, the high tremor periods are when lifting up the new, cooling layer of lava, which must be more than 100m high by now, but otherwise it is open system effusion. Yes, I am looking forward to new drone footage as well!

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          • I got that cartoon sent by a friend when I debated the question whether to give in to the landlords and redecorate the flat on moving out – or to continue threatening them with the law. Guess what, I persevered and won! 🙂

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            • There was a parody of Star Trek made 18 years ago called Galaxy Quest. Funny as Hell. One of the few flicks I watch every single time it is on. Their catch phrase was “Never give up. Never surrender.” So be it with you. Cheers –

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    • Howdy Granyia –

      Saw that last week. Thanks for bringing it forward. You know that same mechanism might also explain the uplift under the TransAntarctic Mountains. Cheers –

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